The Meme Army is a group led by General Jeff Cuphead the Inspritable, Giver of L's during his time as ruler of the Dabiverse. Not much is known about this group, but they were the rival faction to the Monika Guard in the Monikan War.
The Meme Army was formed as a faction during the War of the Orb in support of Jeff Cuphead, and continued to serve him when the universes were split. No characters are explicitly shown to be part of the Meme Army, so it is impossible to know who it consisted of. During the Monikan War, the Meme Army was fighting against the Monika Guard for control over universes. Although it is unknown which universes were controlled by the Meme Army, they do not control Gucciland, Weebland, or The Yeezyverse.
It is unknown what happened to the Meme Army after the defeat of SiIvaGunner, but it is assumed they continued to take universes in Jeff Cuphead's name.